Controller for multi-phase rotary device

ABSTRACT

A controller includes: an inverter having switching devices for converting by a PWM method and supplying an electric power to a multi-phase rotary device; a duty calculator calculating a duty command value with To; a pseudo duty calculator calculating a N-th update duty value based on N-th and (N−1)-th duty command values according to a ratio of To/Tr with a linear compensation method; a comparator comparing the update duty value with a carrier wave to generate an on-off signal of each switching device; and a detector detecting current of each phase with To. The duty calculator changes an average voltage of each phase to make an on-state time of a detection side switching device equal to or longer than minimum. When the on-state time at one phase is smaller than minimum, the pseudo duty calculator outputs a pseudo duty value to detect the current of other phases.

CROSS REFERENCE TO RELATED APPLICATION

This application is based on Japanese Patent Application No. 2012-87813filed on Apr. 6, 2012, the disclosure of which is incorporated herein byreference.

TECHNICAL FIELD

The present disclosure relates to a controller for controlling a driveof a multi-phase rotary device.

BACKGROUND

Conventionally, a controller for driving a multi-phase rotary devicewith a PWM (pulse width modulation) control method is well known. Thecontroller converts a command voltage, which is calculated according tocurrent to be supplied to each phase element in the multi-phase rotarydevice from an electric power converter, to a duty command value. Thus,the controller controls a switching device in the electric powerconverter to switch on and off.

Here, a current detector for detecting current to be supplied to eachphase element in the multi-phase rotary device may includes a Shuntresistor for detecting current flowing through a switching device on ahigh electric potential side or a low electric potential side in theelectric power converter. When the current detector is the Shuntresistor, it is necessary to take sufficient current detection timeincluding convergence time of ringing phenomenon when the switchingdevice switches on and off.

For example, a controller for a three-phase rotary device inJP-B-4715677 selects one of current detecting methods in order to securethe current detection time much longer among two methods. One currentdetecting method provides to detect current in a period, in which all ofswitching devices of three phases disposed on a side connecting to thecurrent detector turns on. The other current detecting method providesto detect current in a period, in which two of switching devicescorresponding to two phases disposed on a side connecting to the currentdetector turns on. In accordance with the selected current detectingmethod, the average voltage of the duty command value is modified toshift to the low voltage side or the high voltage side, so that thevoltage utilization coefficient is improved. Further, the currentdetection time of the multi-phase rotary device is secured.

Here, in order to stabilize the control of the multi-phase rotary deviceand to reduce the noise, the vibration and the torque ripple in the PWMcontrol, it is preferable to bring the calculation cycle of the dutycommand value closer to the cycle of the PWM carrier wave. However, inthis case, when the interruption process of the control process isexecuted very often, i.e., when the number of interruption process timesincreases, the process load also increases. Thus, when multiple dutyupdate values are generated according to the duty command value in onecycle of the control process of the duty command value, the process loadis reduced, and the control of the multi-phase rotary device isstabilized.

In the prior art of JP-B-4715677, the update of the duty value is nottaken into consideration. Accordingly, even if the duty command value ismodified to secure the current detection time sufficiently, the currentdetection time is not always sufficiently secured with respect to theupdate duty command value, which is generated after the duty commandvalue is modified.

SUMMARY

It is an object of the present disclosure to provide a controller for amulti-phase rotary device. The controller stably controls themulti-phase rotary device with reducing a process load. Further, currentdetection time in the controller is sufficiently secured.

According to an example aspect of the present disclosure, a controllerfor a multi-phase rotary device includes: an electric power inverter forconverting an electric power of a direct current power source by a pulsewidth modulation control method and for supplying a converted electricpower to the multi-phase rotary device, the electric power inverterincluding a plurality of switching devices, which have a high voltageside switching device and a low voltage side switching device connectedto each other in a bridge connection manner; a control calculationdevice including: a duty command device for calculating a duty commandvalue, which relates to the pulse width modulation control method, witha predetermined calculation period; and a pseudo duty calculation devicefor calculating a update duty value based on the duty command value withan update period, which has a frequency M times larger than thecalculation period, the M indicative of an integer equal to or largerthan two, the control calculation device outputting the update dutyvalue corresponding to a command voltage of the multi-phase rotarydevice; a carrier wave comparison device for comparing the update dutyvalue with a carrier wave of the pulse width modulation control methodand for generating an on-off signal of each switching device; and acurrent detection device for detecting current of each phase to besupplied to the multi-phase rotary device from the electric powerinverter with the calculation period, the current detection devicearranged between the low voltage side switching device and a negativeterminal of the direct current power source or between the high voltageside switching device and a positive terminal of the direct currentpower source. The duty command device changes an average voltage of eachphase corresponding to the duty command value so that an on-state timeof a detection side switching device corresponding to the duty commandvalue is equal to or longer than a minimum detection time for detectingthe current of each phase with the current detection device. Thedetection side switching device is provided by one of the switchingdevices disposed on a current detection device side. The pseudo dutycalculation device calculates the update duty value, which correspondsto a N-th duty command value, based on the N-th duty command value and a(N−1)-th duty command value in accordance with a ratio between theupdate period and the calculation period with a linear compensationmethod. The duty command device calculates the duty command value Ntimes. The N indicates a natural number. The pseudo duty calculationdevice outputs a pseudo duty value when the on-state time of thedetection side switching device of at least one of phases, whichcorresponds to the update duty value, is smaller than the minimumdetection time. The pseudo duty value is prepared by changing the updateduty value so as to detect the current of all phases other than the atleast one of phases.

In the above controller, since the update duty value is calculated atthe update period equal to one-M-th of the calculation period, thefrequency of comparison between the update duty value and the carrierwave increases without increasing the interruption process of the dutycommand value. Further, the update duty value is calculated by thelinear compensation method, which requires small calculation load.Accordingly, the controller can stably control the rotary device withreducing the calculation load.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the presentdisclosure will become more apparent from the following detaileddescription made with reference to the accompanying drawings. In thedrawings:

FIG. 1 is a diagram showing a controller for a three-phase rotary deviceaccording to first to fifth embodiments;

FIG. 2A is a block diagram showing a process in a control device, andFIG. 2B is a block diagram showing a voltage duty converter;

FIG. 3 is a graph showing a PWM control method;

FIG. 4 is a diagram showing the PWM control method;

FIG. 5 is a diagram showing a voltage vector pattern;

FIG. 6 is a flowchart showing a change process of an average voltage fora duty command value;

FIG. 7 is a diagram showing a lower shift process for detecting currentby a three-phase current method;

FIG. 8 is a diagram showing an upper shift process for detecting currentby a two-phase current method;

FIG. 9 is a graph showing a waveform of the duty command value processedin the change process of the average voltage;

FIG. 10 is a diagram showing a ringing phenomenon in a Shunt resistor;

FIG. 11 is a diagram showing an upper duty limit, at which current isdetectable by the Shunt resistor;

FIG. 12 is a graph showing a relationship between a duty value and a Vovoltage vector generation period in one phase, at which the current isdetected;

FIG. 13 is a timing chart showing a control process and an update of theduty value according to the first and second embodiments;

FIG. 14 is a graph showing a linear compensation process according tothe first and second embodiments;

FIG. 15 is a flowchart showing a pseudo duty calculation processaccording to the first embodiment;

FIG. 16 is a graph showing an upper shift process according to the firstembodiment;

FIG. 17 is a flowchart showing a pseudo duty calculation processaccording to the second embodiment;

FIG. 18 is a graph showing a lower shift process according to the secondembodiment;

FIG. 19 is a timing chart showing a control process and an update of theduty value according to the third and fourth embodiments;

FIG. 20 is a graph showing a linear compensation process according tothe third and fourth embodiments;

FIG. 21 is a flowchart showing a pseudo duty calculation processaccording to the third embodiment;

FIG. 22 is a graph showing an upper shift process according to the thirdembodiment;

FIG. 23 is a flowchart showing a pseudo duty calculation processaccording to the fourth embodiment;

FIG. 24 is a graph showing an A pattern of a lower shift processaccording to the fourth embodiment;

FIG. 25 is a graph showing a B pattern of a lower shift processaccording to the fourth embodiment;

FIG. 26 is a timing chart showing a control process and an update of theduty value according to the fifth embodiment;

FIG. 27 is a flowchart showing a pseudo duty calculation processaccording to the fifth embodiment; and

FIG. 28 is a diagram showing a controller for a three-phase rotarydevice according to a sixth embodiment.

DETAILED DESCRIPTION First Embodiment

As shown in FIG. 1, a ECU (electric control unit) 101 according to afirst embodiment is a controller for controlling a drive of a motor 80,which functions as a multi-phase rotary device. The motor 80 accordingto the present embodiment is a three-phase brushless motor. For example,the motor is used as a steering assist motor for assisting steeringoperation of a driver in an electric power steering system of a vehicle.A rotation angle of the motor 80 detected by a rotation angle sensor 85is converted to an electric angle θ. Then, the electric angle 8 is inputinto a control device 60 of the ECU 101.

The ECU 101 includes an inverter 201, a capacitor 27, Shunt resistors41-43 and the control device 60.

The inverter 201 includes six switching devices 21-26, which areconnected together in a bridge manner. The inverter 201 converts theelectric power from a battery 15 as a direct current power source by aPWM control method, and then, the converted power is supplied to themotor 80. In the present embodiment, the switching device 21-26 is aMOSFET (metal oxide semiconductor field effect transistor).

Thus, the switching devices 21-26 are referred as the MOSFET 21-26.Further, the switching device 21-23 on the high electric potential sideis referred as an upper MOSFET 21-23, and the switching device 24-26 onthe low electric potential side is referred as a lower MOSFET 24-26.

The inverter 201 is connected to a positive side of the battery 15 via apower source line Lp. Further, the inverter 201 is connected to anegative side of the battery 15 via a ground line Lg.

The drain of the upper MOSFET 21-23 is connected to the power sourceline Lp. Further, the source of the upper MOSFET 21-23 is connected tothe drain of the lower MOSFET 24-26. The source of the lower MOSFET24-26 is connected to the ground line Lg via the Shunt resistor 41-43. Aconnection point between the upper MOSFET 21-23 and the lower MOSFET24-26 is connected to one end of the U-phase coil 81, the V-phase coil82, or the W phase coil 83 in the motor 80. A signal generated in acarrier wave comparison device 57 is input into the source of eachMOSFET 21-26, so that a switch between the source and the drain turns onand off.

The capacitor 27 is connected between the power source line Lp and theground line Lg. The capacitor 27 accumulates charges so that thecapacitor 27 assists electric power supply to the MOSFET 21-26.Alternatively, the capacitor 27 limits a noise component such as a surgecurrent.

The Shunt resistor 41-43 as the current detecting device detectscurrent, which is to be supplied to each phase coil 81-83 in the motor80 from the inverter 60, at predetermined intervals, which are the samecycle of the calculation period of a control calculation device 50.Then, the detected current is transferred to the control device 60.Here, in FIG. 1, the Shunt resistors 41-43 are integrally defined as aShunt resistor 40.

In the present embodiment, each Shunt resistor 41-43 is formed betweenthe lower MOSFET 24-26 and th ground line Lg. Accordingly, the lowerMOSFET 24-26 corresponds to the switching device on the detection side.

The control device 60 includes a micro computer 67 and a driving circuit68. The control device 60 controls a whole of the ECU 101.

As shown in FIG. 2, the control device 60 further includes athree-phase/two-phase converter device 51, a control element 52, atwo-phase/three-phase converter device 53, a voltage duty converter 54and a carrier wave comparison device 57. Here, the three-phase/two-phaseconverter device 51, the control element 52, the two-phase/three-phaseconverter device 53, and the voltage duty converter 54 provide thecontrol calculation device 50.

The three-phase/two-phase converter device 51 calculates current Iu, Iv,Iw of each phase according to the current detection value detected bythe Shunt resistor 41-43. Based on the calculated current Iu, Iv, Iw andthe electric angle θ, the three-phase/two-phase converter device 51calculates a d-axis current detection value Id and a q-axis currentdetection value Iq.

The control device 52 calculates a current deviation ΔId between ad-axis command current value Id* and the d-axis current detection valueId and a current deviation ΔIq between a q-axis command current valueIq* and the q-axis current detection value Iq with executing a currentfeedback control method. Further, the control device 52 calculates acommand voltage values Vd*, Vq*, each of which converges the currentdeviation ΔId, ΔIq to be zero.

The two-phase/three-phase converter device 53 calculates three-phasecommand voltages Vu*, Vv*, Vw* based on the command voltages Vd*, Vq*and the electric angle θ, which are calculated by the control device 52.

The voltage duty converter 54 converts the three-phase command voltagesVu*, Vv*, Vw* to the duty values relating to applied voltages to thecoils 81-83 with referenced to the capacitor voltage Vc, and then,inputs the duty values into the carrier wave comparison device 57.

The voltage duty converter 54 includes: a duty command device 55 forinstructing the duty command values DoU, DoV, DoW relating to the PWMcontrol of the inverter 201; and a pseudo duty calculation device 56 forcalculating the update duty value based on the duty command value.

The duty command device 55 further includes: a voltage duty conversiondevice 551 for converting the command voltage to the duty ratio; a deadtime compensation device 552 for setting the dead time; and an averagevoltage changing device 553 for executing the average voltage changingprocess. The duty command device 55 calculates the duty command value atpredetermined calculation intervals.

The pseudo duty calculation device 56 calculates the update period ofthe update duty value, which has a frequency M times larger than thecalculation interval. Here, the factor of M is an integer equal to orlarger than two. In the present embodiment, the factor of M is two. Thecalculation interval and the update period will be explained later.

The carrier wave comparison device 57 compares the update duty valueDrU1, DrV1, DrW1, DrU2, DrV2, DrW2 output from the voltage dutyconverter 54 with the PWM standard signal as a carrier signal of thecarrier wave, and further, generates an on/off signal of each MOSFET21-26 in the inverter 201. In the present embodiment, the carrier waveis a triangle wave having an isosceles triangle shape so that a risingrate is equal to a falling rate.

Next, a general PWM control method will be explained with reference toFIGS. 3 to 5.

As shown in FIG. 3, the duty command signal D includes a U-phase dutycommand signal Du, a V-phase duty command signal Dv and a W-phase dutycommand signal Dw, which are sine wave signals having the substantiallysame amplitude and a different phase. The phases of the U-phase dutycommand signal Du, the V-phase duty command signal Dv and the W-phaseduty command signal Dw are different from each other by 120 degrees. Theaverage between the maximum value of the duty command signal D and theminimum value of the duty command signal D corresponds to the duty of50%.

The PWM standard signal P is a triangle wave signal. In the presentembodiment, the frequency of the PWM standard signal P is 20 kHz, andthe period of the signal P is 50 microseconds. Thus, the period of thesignal P is much shorter than the period of the sine wave in the dutycommand signal D. Here, FIG. 3 schematically shows the PWM standardsignal P so that the number of cycles of the PWM standard signal Pwithin one period of the duty command signal D may be different.Actually, the frequency of the PWM standard signal P is much lager thanin FIG. 3, i.e., the number of cycles of the PWM standard signal Pwithin one period of the duty command signal D is much larger than inFIG. 3.

FIG. 4 shows a partially enlarged view of region K in FIG. 3. In FIG. 4,the magnitude relationship between the PWM standard signal P and theduty command signal D is schematically shown.

In the PWM control process, each phase duty command signal Du, Dv, Dw iscompared with the PWM standard signal P, and then, the on/off signal ofeach MOSFET 21-26 is generated. In the present embodiment, in a sectionthat the PWM standard signal P exceeds each phase duty command signalDu, Dv, Dw, the upper MOSFET 21-23 turns off, and the lower MOSFET 24-26turns on. Further, in a section that each phase duty command signal Du,Dv, Dw exceeds the PWM standard signal P, the upper MOSFET 21-23 turnson, and the lower MOSFET 24-26 turns off. Thus, the upper MOSFET 21-23and the lower MOSFET 24-26 in each phase oppositely turn on and off.

Specifically, for example, in the section KV1, the PWM standard signal Pis disposed lower than the U-phase duty command signal Du, and higherthan the V-phase duty command signal Dv and the W-phase duty commandsignal Dw. Accordingly, in the U-phase, the upper MOSFET 21 turns on,and the lower MOSFET 24 turns off. In the V-phase and the W-phase, theupper MOSFET 22, 23 turns on, and the lower MOSFET 25, 26 turns on.

As shown in FIG. 5, the voltage vector pattern indicative of the on/offstate of the MOSFET in each phase includes eight patterns. During thezero voltage vector period of V0, all of the lower MOSFETS 24-26 inthree phases turn on. During the zero voltage vector period of V7, allof the upper MOSFETS 21-23 in three phases turn on. Accordingly, duringthe zero voltage vector period V0 or the zero voltage vector period ofV7, the voltage is not applied to each phase coil 81-83. On the otherhand, during the effective voltage vector periods V1-V6, one or two ofthe lower MOSFETS 24-26 in three phases turn on, so that the voltage isapplied to each phase coil 81-83.

Next, the average voltage changing process of the duty command valueexecuted by the duty command device 55 will be explained with referenceto FIGS. 6 to 9. The average voltage changing process is disclosed inJP-B-4175677 (corresponding to U.S. Pat. No. 5,831,804).

In the average voltage changing process, one of two methods fordetecting the current to be supplied to the motor 80 from the inverter60 at each phase is selected. A first method provides to detect thecurrent flowing through the Shunt resistors 41-43 at three phases in thezero voltage vector generation period. Here, the zero voltage isreferred as V0, and in the zero voltage vector generation period, all ofthe lower MOSFETS 24-26 at three phases turn on. The first method isdefined as a three-phase current detecting method.

A second method provides to detect the current flowing through two Shuntresistors at two phases corresponding to the low MOSFETS, which turn on,in a period, in which two lower MOSFETS at two phases turn on, and onelower MOSFET at one phase turns off. Further, the second method providesto estimates the current flowing through one Shunt resistor at the onephase corresponding to the lower MOSFET, which turns off, according tothe Kirchhoff law. The second method is defined as a two-phase currentdetecting method. The two-phase current detecting method is executed inthe V1 voltage vector period when the current estimating phase is the Uphase. The two-phase current detecting method is executed in the V3voltage vector period when the current estimating phase is the V phase.The two-phase current detecting method is executed in the V5 voltagevector period when the current estimating phase is the W phase. Thus,the two-phase current detecting method is executed in an odd numbervoltage vector generation period.

In the average voltage changing process, one of the three-phase currentdetecting method and the two-phase current detecting method is selectedin order to secure a longer current detection period. Further, theaverage voltage of the duty command value is displaced (i.e., shifted)to the lower voltage side or the higher voltage side. The detail of theaverage voltage changing process will be explained with reference to theflowchart in FIG. 6. In FIGS. 6, 15, 17, 21, 23, and 27, the word “S”indicates a step.

In step S01 of FIG. 6, the zero voltage vector generation period, whichis a sum of the V0 period and the V7 period, is calculated. Further, theodd number voltage vector generation periods, i.e., the V1, V3 and V5voltage vector generation periods, are calculated. At step S02, the zerovoltage vector generation period is compared with the odd number voltagevector generation periods. When the zero voltage vector generationperiod is longer than or equal to the odd number voltage vectorgeneration periods, i.e., when the determination in step S02 is “YES,”it goes to step S03. At step S03, the average voltage of the dutycommand value is shifted to the low voltage side. Then, in step S04, thecurrent is detected by the three-phase current detecting method in thezero voltage vector generation period.

Here, the process for shifting to the low voltage side in the averagevoltage changing process of the duty command value will be explainedwith reference to FIGS. 7 and 9. For example, at point Kb in FIG. 9, theduty command values of three phases are arranged in descending order ofthe U phase, the V phase and the W phase. In this case, as shown in FIG.9, the average voltage is shifted to the low voltage side in the lowershift step in order to set the duty ratio of the W phase correspondingto the minimum duty command value to be zero. Thus, the duty ratio ofthe U phase corresponding to the maximum duty command value is reduced.Further, the zero voltage vector generation period of V7 before shiftingthe average voltage is added to the zero voltage vector period of V0, sothat the zero voltage vector period of V0 becomes maximum.

When the zero voltage vector generation period is shorter than the oddnumber voltage vector generation periods, i.e., when the determinationin step S02 is “NO,” it goes to step S05. At step S05, the averagevoltage of the duty command value is shifted to the high voltage side.Then, in step S06, the current is detected by the two-phase currentdetecting method in the odd number voltage vector generation periods.

Here, the process for shifting to the high voltage side in the averagevoltage changing process of the duty command value will be explainedwith reference to FIGS. 8 and 9. For example, at point Kt in FIG. 9, theduty command values of three phases are arranged in descending order ofthe U phase, the V phase and the W phase. In this case, as shown in FIG.10, the average voltage is shifted to the high voltage side in the uppershift step in order to set the duty ratio of the U phase correspondingto the maximum duty command value to be 100%. Thus, the zero voltagevector period of V0 before shifting the average voltage is deleted, sothat the V1 voltage vector periods disposed on both sides of the zerovoltage vector period of V0 are integrated to a continuous one V1voltage vector period. As a result, the current is detected in thecontinuous one V1 voltage vector period.

Thus, the average voltage changing process of the duty command valueprovides to secure the current detection time. Here, the average voltagechanging process relates to the duty command value.

On the other hand, the ECU 101 according to the present embodimentgenerates the update duty value based on the duty command value in orderto reduce the noise and the vibration of the motor 80 and to stabilizethe motor operation. Further, the ECU 101 executes the process forsecuring the current detecting time with respect to the update dutyvalue. The pseudo duty calculation device 56 executes these processes.

The pseudo duty calculation device 56 calculates the update duty valuebased on the duty command value according to the linear compensationmethod. The device 56 determines whether the current detection time issufficiently secured with respect to the calculated update duty value.If the current detection time is not sufficiently secured, the device 56corrects the update duty value to be the pseudo duty value.

Here, the minimum detection time for detecting the current with usingthe Shunt resistors 41-43 will be explained with reference to FIGS. 10to 12.

As shown in FIG. 10, the detection current flowing through the Shuntresistor 41-43 exhibits the ringing phenomenon just after the low MOSFETswitches from the off state to the on-state. Thus, after the low MOSFETturns on, the detection starts when two microseconds has elapsed. Here,the ringing phenomenon converges at the detection starting time when twomicroseconds has elapsed since the low MOSFET turns on. Further, it isnecessary to secure the detection time equal to or longer than twomicroseconds. Therefore, the minimum time interval, in which the MOSFETcontinues to turn on, is four microseconds.

Further, as shown in FIG. 11, it is necessary for the time intervalbetween the time, at which the upper MOSFET turns off, and the time, atwhich the lower MOSFET turns on, to include dead time equal to 0.5microseconds. Further, it is necessary for the time interval between thetime, at which the lower MOSFET turns off, and the time, at which theupper MOSFET turns on, to include dead time equal to 0.5 microseconds.Thus, it is necessary to make a total of dead time equal to 1microsecond. Therefore, the time interval, in which the upper MOSFETmaintains in the off-state, is at least five microseconds, which is theminimum detection time for detecting the current.

In the present embodiment, since the period of the carrier wave is 50microseconds, as shown in FIG. 12, the minimum detection time issufficiently secured when the duty ratio is equal to or smaller than90%. Thus, in the present embodiment, the upper duty limit is set to be90%. Thus, when one of the update duty values at three phases exceedsthe upper duty limit of 90%, the process for correcting the update dutyvalue to be the pseudo duty value is executed.

The process executed by the pseudo duty calculation device 56 will beexplained.

First, as shown in FIG. 13, common features between the first embodimentand the second to fifth embodiments will be explained.

In the first to fifth embodiments, the frequency of the control processby the control calculation device 50 is 5 kHz, and the period To of thecalculation is 200 microseconds. Further, the current detection withusing the Shunt resistors 41-43 is performed at a cycle, which is thesame as the calculation period To. The current detection time tIDcoincides with a peak of the carrier wave.

The frequency of the carrier wave is 20 kHz, and the period of thecarrier wave is 50 microseconds. Accordingly, four cycles of the carrierwave are disposed in one cycle of the calculation period To. In thefirst to fourth embodiments, the interruption of the control calculationprocess is performed at a bottom of the carrier wave. In the fifthembodiment, the interruption of the control calculation process isperformed at a top of the carrier wave.

The duty command values of the U phase, the V phase and the W phase,which are calculated at the n-th control calculation process, aredefined as DoU(n), DoV(n), and DoW(n). A group of the update dutyvalues, which are prepared based on the n-th duty command value, arereferred as DrU1(n), DrV1(n), DrW1(n) and so on. Here, when the numberof control calculation process is not specified, i.e., when the numberof the control calculation process is not specified in the duty commandvalues and the update duty values, the indication of (n) is deleted, sothat the duty command values are defined as DoU, DoV(n), and DoW(n), andthe update duty values are referred as DrU1, DrV1, DrW1 and so on. Whenthe phase is not specified, the duty command value is referred as Do,and the update duty value is referred as Dr.

The update duty value, which is corrected to be the pseudo duty value inthe upper shift process and the lower shift process, is referred asDrU1′(n), DrV1′(n) and DrW1′(n).

Specific features in the first embodiment will be explained withreference to FIG. 13.

As shown in FIG. 13, the pseudo duty calculation device 56 generates theupdate duty value Dr twice in one cycle of the calculation period. Thus,the update frequency is 10 kHz, which is twice larger than the controlcalculation frequency, i.e., 5 kHz. The update period Tr, which is 100microseconds, is a half of the calculation period To, which is 200microseconds, as described in an equation of No. 1

Tr=(½)To  (Equation No. 1)

The update duty value corresponding to the duty command value Do(n),which is generated by the n-th control calculation, is calculated suchthat the first update duty value Dr1(n) is calculated at the firstupdate time tr1(n) after the time interval of (½)To has elapsed from thecontrol calculation time to(n), and the second update duty value Dr2(n)is calculated at the second update time tr2(n) after the update periodTr has elapsed from the first update time tr1(n). The first update dutyvalue Dr1(n) is effective by the second update time tr2. The currentdetection time tID is arranged in the effective period of the firstupdate duty value Dr1(n).

As shown in FIG. 14, for example, the first and second update dutyvalues DrU1(n), DrU2(n) of the U phase are calculated by the linearcompensation method in accordance with the ratio between the updateperiod Tr and the calculation period To, based on the (n−1)-th dutycommand value DoU(n−1) and the n-th duty command value DoU(n). Thus, thefollowing equations No. 2 and No. 3 are obtained.

DrU1(n)=DoU(n−1)+{DoU(n)−DoU(n−1)}/2  (Equation No. 2)

DrU2(n)=DoU(n)  (Equation No. 3)

As shown in FIG. 15, in the pseudo duty calculation process according tothe first embodiment, the update duty value Dr1, Dr2 of each phase iscalculated by the linear compensation method at step S10. Then, at stepS11, the first update duty value Dr1 is checked. Here, the first updateduty value Dr1 is effective at the current detection time tID.

At step S11, it is determined whether the first update duty value DrU1,DrV1, DrW1 of each phase exceeds the upper duty limit DL and is disposedin a prohibition range, which is smaller than 100. When one of the firstupdate duty values DrU1, DrV1, DrW1 is disposed in the prohibitionrange, i.e., when the determination in step S11 is “YES,” it goes tostep S12, and at step S12, the upper shift process is executed.

When all of the first update duty values DrU1, DrV1, DrW1 are notdisposed in the prohibition range, i.e., when the determination in stepS11 is “NO,” the pseudo duty calculation process is terminated. In thiscase, the first update duty values DrU1, DrV1, DrW1 are output withoutcorrecting.

The upper shift process will be explained assuming that the first updateduty value DrU1 of the U phase is the largest among the first updateduty values DrU1, DrV1, DrW1, and the first update duty value DrU1 isdisposed in the prohibition range.

As shown in FIG. 16, in the upper shift process, the first update dutyvalue DrU1 of the U phase is corrected to be equal to the second updateduty value DrU2, so that the first update duty value DrU1 as the pseudoduty value is output. Here, in the average voltage changing process ofthe duty command device 55, when the on-state time interval of the lowMOSFETS at the V phase and the W phase corresponding to the voltagevector V1 is longer than the on-state time of the low MOSFETS at allphases corresponding to the voltage vector V0, the duty command valueDoU(n) is shifted to the upper side, and the shifted duty command valueDoU(n) is output. Accordingly, since the second update duty value DrU2is 100%, the first update duty value DrU1 becomes 100%.

Further, each of the first update duty values DrV1, DrW1 at the V phaseand the W phase are corrected to be equal to the second update dutyvalues DrV2, DrW2 so that the first update duty values DrV1, DrW1 as thepseudo duty value is output. Thus, the following equations No. 4 to No.6 are obtained.

DrU1′(n)=DrU2(n)=100  (Equation No. 4)

DrV1′(n)=DrV2(n)  (Equation No. 5)

DrW1′(n)=DrW2(n)  (Equation No. 6)

Thus, the V1 voltage vector period, in which the lower MOSFETS of the Vphase and the W phase turn on, is secured, and then, the current isdetected. Further, the current flowing through the U phase is estimatedby Kirchhoff law.

In the first embodiment, since the update duty value Dr is calculatedaccording to the update period Tr, which is a half of the calculationperiod To, repetition (i.e., the number of times) for comparing the dutyratio and the carrier wave increases without increasing the number ofthe interruption processes of the duty command value To. Further, theupdate duty value Dr is calculated by the linear compensation method,which has a low calculation load. Accordingly, the motor 80 is stablycontrolled with reducing the calculation load. Therefore, the noise, thevibration and the torque ripple are reduced.

Further, the average voltage changing process for securing the currentdetection time sufficiently is primarily executed with respect to theduty command value Do, the average voltage changing process is secondlyexecuted with respect to the first update duty value Dr1 at the currentdetection time tID. Thus, the current detection time for the Shuntresistors 41-43 is appropriately secured. Thus, the current to besupplied to the motor 80 from the inverter 201 is surely detected.

Second Embodiment

A second embodiment will be explained with reference to FIGS. 13-14 and17-18. The update timing of the update duty value Dr and the calculationmethod of the update duty value Dr shown in FIGS. 13 and 14 are similarto the first embodiment.

As shown in FIG. 17, in the pseudo duty calculation process according tothe second embodiment, the update duty value Dr1, Dr2 of each phase iscalculated by the linear compensation method at step S20. Then, at stepsS211 to S231, the first update duty value of each phase is checked inturn. Here, the first update duty value Dr1 is effective at the currentdetection time tID.

At step S211, it is determined whether the first update duty value DrU1of the U phase exceeds the upper duty limit DL and is disposed in aprohibition range, which is smaller than 100. When the first update dutyvalue DrU1 is disposed in the prohibition range, i.e., when thedetermination in step S211 is “YES,” it goes to step S212, and at stepS212, the lower shift process is executed.

When the first update duty value DrU1 is not disposed in the prohibitionrange, i.e., when the determination in step S211 is “NO,” it goes tostep S221. At step S221, it is determined whether the first update dutyvalue DrV1 of the V phase exceeds the upper duty limit DL and isdisposed in a prohibition range, which is smaller than 100. When thefirst update duty value DrV1 is disposed in the prohibition range, i.e.,when the determination in step S221 is “YES,” it goes to step S222, andat step S222, the lower shift process is executed.

When the first update duty value DrV1 is not disposed in the prohibitionrange, i.e., when the determination in step S221 is “NO,” it goes tostep S231. At step S231, it is determined whether the first update dutyvalue DrW1 of the W phase exceeds the upper duty limit DL and isdisposed in a prohibition range, which is smaller than 100. When thefirst update duty value DrW1 is disposed in the prohibition range, i.e.,when the determination in step S231 is “YES,” it goes to step S232, andat step S232, the lower shift process is executed.

When the first update duty value DrW1 is not disposed in the prohibitionrange, i.e., when the determination in step S231 is “NO,” the pseudoduty calculation process ends. In this case, the first update dutyvalues DrU1, DrV1, DrW1 are output without correcting.

The lower shift process will be explained assuming that the first updateduty value DrU1 of the U phase is the largest among the first updateduty values DrU1, DrV1, DrW1, and the first update duty value DrU1 isdisposed in the prohibition range.

As shown in FIG. 18, in the lower shift process, the first update dutyvalue DrU1 of the U phase is corrected to be equal to the upper dutylimit DL, so that the first update duty value DrU1 as the pseudo dutyvalue is output. In this case, the lower shift amount of the firstupdate duty value DrU1 is defined as a first lower shift amount ΔU1. Thefirst lower shift amount ΔU1 is negative. Thus, the equations No. 7 andNo. 8 are obtained.

DrU1′(n)=DL  (Equation No. 7)

ΔU1=DL−DrU1<0  (Equation No. 8)

Further, regarding the V phase and the W phase, as described equationsNo. 9 and No. 10, the first lower shift amount ΔU1 is added to the firstupdate duty value DrV1, DrW1 so that the lower shift step is executed.

DrV1′(n)=DrV1+ΔU1  (Equation No. 9)

DrW1′(n)=DrW1+ΔU1  (Equation No. 10)

Thus, the on-state time of the lower MOSFET of the U phase, which hasthe largest first update duty value DrU1 at the first update time tr1,is set to be the minimum detection time. Then, the current is detectedin the V0 voltage vector period, in which the lower MOSFETS of threephases turn on.

The second embodiment provides similar effects to the first embodiment.

Third Embodiment

Next, a third embodiment will be explained with reference to FIGS. 19 to22.

As show in FIG. 19, the pseudo duty calculation device 56 generates theupdate duty value Dr four times in one cycle of the calculation periodTo. The update frequency is 20 kHz, which is four times larger than thecontrol calculation frequency, i.e., 5 kHz. The update period Tr, whichis 50 microseconds, is a one-fourth of the calculation period To whichis 200 microseconds, as described in an equation of No. 11.

Tr=(¼)To  (Equation No. 11)

The update duty value corresponding to the duty command value Do(n),which is generated by the n-th control calculation, is calculated suchthat the first update duty value Dr1(n) is calculated at the firstupdate time tr1(n) after the time interval of (½)To has elapsed from thecontrol calculation time to(n). Then, the second update duty valueDr2(n) is calculated at the second update time tr2(n) after the updateperiod Tr has elapsed from the first update time tr1(n). Then, the thirdupdate duty value Dr3(n) is calculated at the third update time tr3(n)after the update period Tr has elapsed from the second update timetr2(n). Then, the fourth update duty value Dr4(n) is calculated at thefourth update time tr4(n) after the update period Tr has elapsed fromthe third update time tr3(n).

The current detection time tID coincides with the peak of the carrierwave between the second update time tr2 and the third updated time tr3.Accordingly, the second update duty value Dr2(n) is effective at thecurrent detection time tID.

As shown in FIG. 20, for example, the first to fourth update duty valuesDrU1(n), DrU2(n), DrU3(n), DrU4(n) of the U phase are calculated by thelinear compensation method in accordance with the ratio between theupdate period Tr and the calculation period To, based on the (n−1)-thduty command value DoU(n−1) and the n-th duty command value DoU(n).Thus, the following equations No. 12 to No. 15 are obtained.

DrU1(n)=DoU(n−1)+{DoU(n)−DoU(n−1)}/4  (Equation No. 12)

DrU2(n)=DoU1(n)+{DoU(n)−DoU(n−1)}/4  (Equation No. 13)

DrU3(n)=DoU2(n)+{DoU(n)−DoU(n−1)}/4  (Equation No. 14)

DrU4(n)=DoU(n)  (Equation No. 15)

As shown in FIG. 21, in the pseudo duty calculation process according tothe third embodiment, the update duty value Dr1, Dr2, Dr3, Dr4 of eachphase is calculated by the linear compensation method at step S30. Then,at step S31, the second update duty value Dr2 is checked. Here, thesecond update duty value Dr2 is effective at the current detection timetID.

At step S31, it is determined whether the second update duty value DrU2,DrV2, DrW2 of each phase exceeds the upper duty limit DL and is disposedin a prohibition range, which is smaller than 100. When one of thesecond update duty values DrU2, DrV2, DrW2 is disposed in theprohibition range, i.e., when the determination in step S31 is “YES,” itgoes to step S32, and at step S32, the upper shift process is executed.

When all of the second update duty values DrU2, DrV2, DrW2 are notdisposed in the prohibition range, i.e., when the determination in stepS31 is “NO,” the pseudo duty calculation process is terminated. In thiscase, the second update duty values DrU2, DrV2, DrW2 are output withoutcorrecting.

The upper shift process will be explained assuming that the secondupdate duty value DrU2 of the U phase is the largest among the secondupdate duty values DrU2, DrV2, DrW2, and the second update duty valueDrU2 is disposed in the prohibition range.

As shown in FIG. 22, in the upper shift process, the second update dutyvalue DrU2 of the U phase and the third update duty value DrU3 justafter the current detection time tID are corrected to be equal to thefourth update duty value DrU4, so that the second update duty value DrU2and the third update duty value DrU3 as the pseudo duty value areoutput. Here, in the average voltage changing process of the dutycommand device 55, when the on-state time interval of the low MOSFETS atthe V phase and the W phase corresponding to the voltage vector V1 islonger than the on-state time of the low MOSFETS at all phasescorresponding to the voltage vector V0, the duty command value DoU(n) isshifted to the upper side to be 100%, and the shifted duty command valueDoU(n) is output. Accordingly, since the fourth update duty value DrU4is 100%, the second and third update duty values DrU2, DrU3 becomes100%.

Further, each of the second update duty values DrV2, DrW2 and the thirdupdate duty values DrV3, DrW3 at the V phase and the W phase iscorrected to be equal to the fourth update duty values DrV4, DrW,respectively, so that the second and third update duty values DrV2,DrW2, DrV3, DrW3 as the pseudo duty value are output.

Thus, the V1 voltage vector period, in which the lower MOSFETS of the Vphase and the W phase turn on, is secured, and then, the current isdetected. Further, the current flowing through the U phase is estimatedby Kirchhoff law.

In the third embodiment, the frequency of the update period Tr is twicelarger than the first embodiment. Thus, the motor 80 is stablycontrolled. Therefore, the noise, the vibration and the torque rippleare reduced.

Fourth Embodiment

A fourth embodiment will be explained with reference to FIGS. 13-14 and19-20 and 23-24. The update timing of the update duty value Dr and thecalculation method of the update duty value Dr shown in FIGS. 19 and 20are similar to the third embodiment.

As shown in FIG. 23, in the pseudo duty calculation process according tothe fourth embodiment, the update duty values Dr1, Dr2, Dr3, Dr4 of eachphase is calculated by the linear compensation method at step S40. Then,at steps S411 to S432, the first update duty value and the second updateduty value of each phase are checked in turn. Here, the second updateduty value Dr2 is effective at the current detection time tID.

At step S411, it is determined whether the second update duty value DrU2of the U phase exceeds the upper duty limit DL and is disposed in aprohibition range, which is smaller than 100. When the second updateduty value DrU2 is disposed in the prohibition range, i.e., when thedetermination in step S411 is “YES,” it goes to step S412, and at stepS412, it is determined whether the first update duty value DrU1 of the Uphase is equal to or smaller than the upper duty limit DL.

When the second update duty value DrU2 is disposed in the prohibitionrange, i.e., the determination in step S411 is “YES,” and the firstupdate duty value DrU1 of the U phase is equal to or smaller than theupper duty limit DL, i.e., the determination in step S412 is “YES,” itgoes to step S413, and at step S413, the A pattern of the lower shiftprocess is executed. When the second update duty value DrU2 is disposedin the prohibition range, i.e., the determination in step S411 is “YES,”and the first update duty value DrU1 of the U phase exceeds the upperduty limit DL and is disposed in the prohibition range, i.e., thedetermination in step S412 is “NO,” it goes to step S414, and at stepS414, the B pattern of the lower shift process is executed.

When the second update duty value DrU2 is not disposed in theprohibition range, i.e., when the determination in step S411 is “NO,”the second update duty value DrV2 of the V phase and the first updateduty value DrV1 of the V phase are similarly checked at step S421 andstep S422. When the second update duty value DrV2 is disposed in theprohibition range, i.e., when the determination in step S421 is “YES,”one of the A pattern of the lower shift process and the B pattern of thelower shift process is executed at step S423 or step S424.

When the second update duty value DrV2 of the V phase is not disposed inthe prohibition range, i.e., when the determination in step S421 is“NO,” the second update duty value DrW2 of the W phase and the firstupdate duty value DrW1 of the W phase are similarly checked at step S431and step S432. When the second update duty value DrW2 is disposed in theprohibition range, i.e., when the determination in step S431 is “YES,”one of the A pattern of the lower shift process and the B pattern of thelower shift process is executed at step S433 or step S434.

When the second update duty value DrW2 of the W phase is not disposed inthe prohibition range, i.e., when the determination in step S431 is“NO;” the pseudo duty calculation process ends. In this case, the secondupdate duty values DrU2, DrV2, DrW2 are output without correcting.

The A pattern lower shift process will be explained assuming that thesecond update duty value DrU2 of the U phase is the largest among thesecond update duty values DrU2, DrV2, DrW2, and the second update dutyvalue DrU2 is disposed in the prohibition range.

As shown in FIG. 24, in the A pattern lower shift process, the secondupdate duty value DrU2 of the U phase is corrected to be equal to theupper duty limit DL, so that the second update duty value DrU2 as thepseudo duty value is output. Further, the third update duty value DrU3is re-calculated by the linear compensation method based on the upperduty limit DL and the fourth update duty value DrU4. In this case, thelower shift amount of the second update duty value DrU2 is defined as asecond lower shift amount ΔU2, and the lower shift amount of the thirdupdate duty value DrU3 is defined as a third lower shift amount ΔU3.

Further, regarding the V phase and the W phase, the second update dutyvalues DrV2, DrW2 are shifted to the lower side by the second lowershift amount ΔU2, respectively. Furthermore, the third update dutyvalues DrV3, DrW3 are shifted to the lower side by the third lower shiftamount ΔU3, respectively.

Thus, the on-state time of the lower MOSFET of the U phase, which hasthe largest second update duty value DrU2 at the second update time tr2,is set to be the minimum detection time. Then, the current is detectedin the V0 voltage vector period, in which the lower MOSFETS of threephases turn on.

Then, the B pattern lower shift process will be explained assuming thatthe second update duty value DrU2 of the U phase is the largest amongthe second update duty values DrU2, DrV2, DrW2, and the first and secondupdate duty values DrU1, DrU2 are disposed in the prohibition range.

As shown in FIG. 25, in the B pattern lower shift process, the first andsecond update duty values DrU1, DrU2 of the U phase are corrected to beequal to the upper duty limit DL, so that the first and second updateduty values DrU1, DrU2 as the pseudo duty value are output. Further, thethird update duty value DrU3 is re-calculated by the linear compensationmethod based on the upper duty limit DL and the fourth update duty valueDrU4. In this case, the lower shift amount of the first update dutyvalue DrU1 is defined as a first lower shift amount ΔU1, the lower shiftamount of the second update duty value DrU2 is defined as a second lowershift amount ΔU2, and the lower shift amount of the third update dutyvalue DrU3 is defined as a third lower shift amount ΔU3.

Further, regarding the V phase and the W phase, the first update dutyvalues DrV1, DrW1 are shifted to the lower side by the first lower shiftamount ΔU1, respectively. Further, the second update duty values DrV2,DrW2 are shifted to the lower side by the second lower shift amount ΔU2,respectively. Furthermore, the third update duty values DrV3, DrW3 areshifted to the lower side by the third lower shift amount ΔU3,respectively.

Thus, the on-state time of the lower MOSFET of the U phase, which hasthe largest second update duty value DrU2 at the second update time tr2,is set to be the minimum detection time. Then, the current is detectedin the V0 voltage vector period, in which the lower MOSFETS of threephases turn on.

The fourth embodiment provides similar effects to the third embodiment.Further, the third update duty value Dr3 is re-calculated by the linearcompensation method according to the second update duty value Dr2 andthe fourth update duty value Dr4. Thus, the update duty value Dr can bechanged with a predetermined gradient between the second update time tr2and the fourth update time tr4.

Fifth Embodiment

Next, a fifth embodiment will be explained with reference to FIGS. 26 to27.

As shown in FIG. 26, in the fifth embodiment, the update period of theupdate duty value Dr is one-fourth of the calculation period, which issimilar to the third and fourth embodiments. Further, the calculationmethod of the update duty value Dr is similar to the third and fourthembodiments.

In the fifth embodiment, the control calculation time to and the updatetime tr1-tr4 are disposed at a peak of the carrier wave, which isdifferent from the bottom of the carrier wave in the third and fourthembodiments. Accordingly, the current detection time tID coincides withthe second update time tr2. Specifically, the current is detected attime when the update duty value is switched from the first update dutyvalue Dr1 to the second update duty value Dr2.

In the above case, when the current is detected in three phases, it isnecessary to satisfy a condition that both of the first update dutyvalue Dr1 and the second update duty value Dr2 before and after thecurrent detection time tID are equal to or smaller than the upper dutylimit DL. Accordingly, in a flowchart of FIG. 27, it is determinedwhether the B pattern lower shift process is executed, which is shown inFIG. 23.

As shown in FIG. 27, in the pseudo duty calculation process according tothe fifth embodiment, the update duty value Dr1 to Dr4 of each phase iscalculated by the linear compensation method at step S50. Then, thefirst and second update duty values of each phase are checked in turn atsteps S511 to S531.

At step S511, it is determined whether the first updated duty value DrU1or the second update duty value DrU2 of the U phase exceeds the upperduty limit DL and is disposed in a prohibition range, which is smallerthan 100. When at least one of the first updated duty value DrU1 and thesecond update duty value DrU2 is disposed in the prohibition range,i.e., when the determination in step S511 is “YES,” it goes to stepS512, and at step S512, the B pattern lower shift process is executed.

When both of the first updated duty value DrU1 and the second updateduty value DrU2 are not disposed in the prohibition range, i.e., whenthe determination in step S511 is “NO,” it goes to step S521. At stepS521, it is determined whether the first updated duty value DrV1 or thesecond update duty value DrV2 of the V phase exceeds the upper dutylimit DL and is disposed in a prohibition range, which is smaller than100. When at least one of the first updated duty value DrV1 and thesecond update duty value DrV2 is disposed in the prohibition range,i.e., when the determination in step S521 is “YES,” it goes to stepS522, and at step S522, the B pattern lower shift process is executed.

When both of the first updated duty value DrV1 and the second updateduty value DrV2 of the V phase are not disposed in the prohibitionrange, i.e., when the determination in step S521 is “NO,” it goes tostep S531. At step S531, it is determined whether the first updated dutyvalue DrW1 or the second update duty value DrW2 of the W phase exceedsthe upper duty limit DL and is disposed in a prohibition range, which issmaller than 100. When at least one of the first updated duty value DrW1and the second update duty value DrW2 is disposed in the prohibitionrange, i.e., when the determination in step S531 is “YES,” it goes tostep S532, and at step S532, the B pattern lower shift process isexecuted.

When both of the first updated duty value DrW1 and the second updateduty value DrW2 of the W phase are not disposed in the prohibitionrange, i.e., when the determination in step S531 is “NO,” the pseudoduty calculation process ends. In this case, the first updated dutyvalues DrU1, DrV1, DrW1 and the second update duty values DrU2, DrV2,DrW2 are output without correcting.

The B pattern lower shift process is similar to FIG. 25 according to thefourth embodiment.

In the fifth embodiment, even when the current is detected at time whenthe update duty value is switched, it is determined whether both of theupdate duty values before and after switching are disposed in theprohibition range. Thus, the fifth embodiment provides the effects ofthe first to fourth embodiments.

Sixth Embodiment

Next, a sixth embodiment will be explained with reference to FIG. 28.

In a ECU 102 according to the sixth embodiment, the Shunt resistors41-43 of the inverter 202 are disposed between the upper MOSFETS 21-23and the power source line Lp, respectively, which is different from theECU 101 according to the first embodiment. Accordingly, in the sixthembodiment, the upper MOSFETS 21-23 correspond to the detection sideswitching device.

The control calculation process and the pseudo duty calculation processaccording to the sixth embodiment are opposite to the first to fifthembodiments.

When the current is detected by the three-phase current detectionmethod, in the sixth embodiment, the lower duty limit in a case wherethe V7 zero voltage vector period becomes the minimum detection time isconsidered, which corresponds to the upper duty limit in a case wherethe V0 zero voltage vector period becomes the minimum detection timeaccording to the first to fifth embodiments. The update duty value Dr ofeach phase is shifted on an upper side so that the V7 zero voltagevector period, in which the upper MOSFETS of all three phases turn on,becomes equal to or larger than the minimum detection time.

Specifically, the minimum update duty value Dr among the update dutyvalues of three phases is corrected to be the lower duty limit at thecurrent detection time tID. In this case, the upper shift amount isadded to the update duty values of other two phases.

When the current is detected by the two-phase current detection method,in the sixth embodiment, the update duty value Dr of each phase isshifted to the lower side so that the current is detected in V2, V4 andV6 even number voltage vector generation periods, in which the upperMOSFETS of two of three phases turn on.

Specifically, the minimum update duty value Dr among the update dutyvalues of three phases is set to be zero % at the current detection timetID. Further, the update duty values of other two phases is changed tonew update values of respective phases corresponding to the update time,at which the minimum update value becomes zero.

(Modifications)

The calculation period and the update frequency and the like accordingto the above embodiments are merely example numerical values. Thus, theymay be different in the above embodiments as long as the update periodTr of the update duty value is one-m-th of the calculation period. Here,the m-th indicates the ordinal number equal to or larger than two.

In the above embodiments, the pseudo duty calculation is performed witha period shorter than the control calculation. Alternatively, the updateduty value may be calculation preliminary in the control calculationprocess. Only the update may be performed with a period of one-m-th ofthe calculation period of To. The term “m” represents an integer equalto or larger than two.

The pseudo duty value for correcting the minimum update duty value amongthe update duty values of three phases may be substantially equal to theupper duty limit DL in the lower shift process executed by the pseudoduty calculation device. For example, the pseudo duty value may be avalue smaller than the upper duty limit DL by 1%. Thus, the pseudo dutyvalue may be smaller than the upper duty limit DL.

The current detection device may be different from the Shunt resistor aslong as the current detection device detects the current flowing throughthe switching device on the high potential side or the low potentialside in the electric power converter.

The switching device may be a device other than the MOSFET. For example,the switching device may be a field effect transistor other than theMOSFET or the IGBT.

The control unit of the ECU executes a d-q conversion process in theabove embodiments. Alternatively, the control unit of the ECU mayexecute a process other than the d-q conversion process. Further, theprocesses in the carrier wave comparison device 57 and the likeaccording to the above embodiments are performed by a software processin the micro computer 67. Alternatively, the processes may be performedby a hardware element.

The carrier wave is a triangle wave having an isosceles triangle shapeso that a rising rate is equal to a falling rate in the aboveembodiments. Alternatively, the carrier wave may be different from thetriangle wave. For example, the carrier wave may be a saw-tooth wave.

In the above embodiments, the number of phases in the multi-phase rotarydevice is three. Alternatively, the number of phases may be four ormore.

In the above embodiments, the controller for the multi-phase rotarydevice is a control device of the motor in the electric power steeringsystem. Alternatively, the controller may be used for a multi-phasemotor or a control device of an electric power generator.

The above disclosure has the following aspects.

According to an example aspect of the present disclosure, a controllerfor a multi-phase rotary device includes: an electric power inverter forconverting an electric power of a direct current power source by a pulsewidth modulation control method and for supplying a converted electricpower to the multi-phase rotary device, the electric power inverterincluding a plurality of switching devices, which have a high voltageside switching device and a low voltage side switching device connectedto each other in a bridge connection manner; a control calculationdevice including: a duty command device for calculating a duty commandvalue, which relates to the pulse width modulation control method, witha predetermined calculation period; and a pseudo duty calculation devicefor calculating a update duty value based on the duty command value withan update period, which has a frequency M times larger than thecalculation period, the M indicative of an integer equal to or largerthan two, the control calculation device outputting the update dutyvalue corresponding to a command voltage of the multi-phase rotarydevice; a carrier wave comparison device for comparing the update dutyvalue with a carrier wave of the pulse width modulation control methodand for generating an on-off signal of each switching device; and acurrent detection device for detecting current of each phase to besupplied to the multi-phase rotary device from the electric powerinverter with the calculation period, the current detection devicearranged between the low voltage side switching device and a negativeterminal of the direct current power source or between the high voltageside switching device and a positive terminal of the direct currentpower source. The duty command device changes an average voltage of eachphase corresponding to the duty command value so that an on-state timeof a detection side switching device corresponding to the duty commandvalue is equal to or longer than a minimum detection time for detectingthe current of each phase with the current detection device. Thedetection side switching device is provided by one of the switchingdevices disposed on a current detection device side. The pseudo dutycalculation device calculates the update duty value, which correspondsto a N-th duty command value, based on the N-th duty command value and a(N−1)-th duty command value in accordance with a ratio between theupdate period and the calculation period with a linear compensationmethod. The duty command device calculates the duty command value Ntimes. The N indicates a natural number. The pseudo duty calculationdevice outputs a pseudo duty value when the on-state time of thedetection side switching device of at least one of phases, whichcorresponds to the update duty value, is smaller than the minimumdetection time. The pseudo duty value is prepared by changing the updateduty value so as to detect the current of all phases other than the atleast one of phases.

In the above controller, since the update duty value is calculated atthe update period equal to one-M-th of the calculation period, thefrequency of comparison between the update duty value and the carrierwave increases without increasing the interruption process of the dutycommand value. Further, the update duty value is calculated by thelinear compensation method, which requires small calculation load.Accordingly, the controller can stably control the rotary device withreducing the calculation load.

Further, the duty command device changes the average voltage of eachphase with respect to the duty command value in process for securing thecurrent detection time. Further, the pseudo duty calculation deviceoutputs the pseudo duty value with respect to the update duty value,which is calculated based on the duty command value by the linearcompensation method, in the process for securing the current detectionprocess.

Alternatively, the multi-phase rotary device may be a three-phase rotarydevice. The current detection device is disposed between the low voltageside switching device and the negative terminal of the direct currentsource. The duty command device changes the average voltage of threephases corresponding to the duty command value so that the current isdetected in a longer one of (i) the on-state time of the low voltageside switching devices of all three phases corresponding to the dutycommand value and (ii) the on-state time of the low voltage sideswitching devices of two phases corresponding to the duty command value.The pseudo duty calculation device outputs the pseudo duty value, whichis prepared by increasing the update duty value of each phase so as todetect the current of all phases other than the at least one of phaseswithin the on-state time of the low voltage side switching devices oftwo phases other than the at least one of phases, when the on-state timeof the low voltage side switching device of at least one of phases,which corresponds to the update duty value, is smaller than the minimumdetection time. In this case, the process for changing the averagevoltage in order to secure the current detection time is performedprimarily with respect to the duty command value. Then, the process forchanging the average voltage is secondly performed with respect to theupdate duty value at the timing of detecting current. Thus, the currentdetection time is appropriately secured. Thus, the current supplied tothe multi-phase rotary device from the electric power inverter is surelydetected.

Alternatively, the multi-phase rotary device may be a three-phase rotarydevice. The current detection device is disposed between the low voltageside switching device and the negative terminal of the direct currentsource. The duty command device changes the average voltage of threephases corresponding to the duty command value so that the current isdetected in a longer one of (i) the on-state time of the low voltageside switching devices of all three phases corresponding to the dutycommand value and (ii) the on-state time of the low voltage sideswitching devices of two phases corresponding to the duty command value.The pseudo duty calculation device outputs the pseudo duty value, whichis prepared by decreasing the update duty value of each phase so as tomake the on-state time of the low voltage side switching devices of allthree phases longer than the minimum detection time, when the on-statetime of the low voltage side switching device of at least one of phases,which corresponds to the update duty value, is smaller than the minimumdetection time. In this case, the process for changing the averagevoltage in order to secure the current detection time is performedprimarily with respect to the duty command value. Then, the process forchanging the average voltage is secondly performed with respect to theupdate duty value at the timing of detecting current. Thus, the currentdetection time is appropriately secured. Thus, the current supplied tothe multi-phase rotary device from the electric power inverter is surelydetected.

While the present disclosure has been described with reference toembodiments thereof, it is to be understood that the disclosure is notlimited to the embodiments and constructions. The present disclosure isintended to cover various modification and equivalent arrangements. Inaddition, while the various combinations and configurations, othercombinations and configurations, including more, less or only a singleelement, are also within the spirit and scope of the present disclosure.

What is claimed is:
 1. A controller for a multi-phase rotary devicecomprising: an electric power inverter for converting an electric powerof a direct current power source by a pulse width modulation controlmethod and for supplying a converted electric power to the multi-phaserotary device, the electric power inverter including a plurality ofswitching devices, which have a high voltage side switching device and alow voltage side switching device connected to each other in a bridgeconnection manner; a control calculation device including: a dutycommand device for calculating a duty command value, which relates tothe pulse width modulation control method, with a predeterminedcalculation period; and a pseudo duty calculation device for calculatinga update duty value based on the duty command value with an updateperiod, which has a frequency M times larger than the calculationperiod, the M indicative of an integer equal to or larger than two, thecontrol calculation device outputting the update duty valuecorresponding to a command voltage of the multi-phase rotary device; acarrier wave comparison device for comparing the update duty value witha carrier wave of the pulse width modulation control method and forgenerating an on-off signal of each switching device; and a currentdetection device for detecting current of each phase to be supplied tothe multi-phase rotary device from the electric power inverter with thecalculation period, the current detection device arranged between thelow voltage side switching device and a negative terminal of the directcurrent power source or between the high voltage side switching deviceand a positive terminal of the direct current power source, wherein: theduty command device changes an average voltage of each phasecorresponding to the duty command value so that an on-state time of adetection side switching device corresponding to the duty command valueis equal to or longer than a minimum detection time for detecting thecurrent of each phase with the current detection device; the detectionside switching device is provided by one of the switching devicesdisposed on a current detection device side; the pseudo duty calculationdevice calculates the update duty value, which corresponds to a N-thduty command value, based on the N-th duty command value and a (N−1)-thduty command value in accordance with a ratio between the update periodand the calculation period with a linear compensation method; the dutycommand device calculates the duty command value N times; the Nindicates a natural number; the pseudo duty calculation device outputs apseudo duty value when the on-state time of the detection side switchingdevice of at least one of phases, which corresponds to the update dutyvalue, is smaller than the minimum detection time; and the pseudo dutyvalue is prepared by changing the update duty value so as to detect thecurrent of all phases other than the at least one of phases.
 2. Thecontroller according to claim 1, wherein: the multi-phase rotary deviceis a three-phase rotary device; the current detection device is disposedbetween the low voltage side switching device and the negative terminalof the direct current power source; the duty command device changes theaverage voltage of three phases corresponding to the duty command valueso that the current is detected in a longer one of (i) the on-state timeof the low voltage side switching devices of all three phasescorresponding to the duty command value and (ii) the on-state time ofthe low voltage side switching devices of two phases corresponding tothe duty command value; and the pseudo duty calculation device outputsthe pseudo duty value, which is prepared by increasing the update dutyvalue of each phase so as to detect the current of all phases other thanthe at least one of phases within the on-state time of the low voltageside switching devices of two phases other than the at least one ofphases, when the on-state time of the low voltage side switching deviceof at least one of phases, which corresponds to the update duty value,is smaller than the minimum detection time.
 3. The controller accordingto claim 1, wherein: the multi-phase rotary device is a three-phaserotary device; the current detection device is disposed between the lowvoltage side switching device and the negative terminal of the directcurrent power source; the duty command device changes the averagevoltage of three phases corresponding to the duty command value so thatthe current is detected in a longer one of (i) the on-state time of thelow voltage side switching devices of all three phases corresponding tothe duty command value and (ii) the on-state time of the low voltageside switching devices of two phases corresponding to the duty commandvalue; and the pseudo duty calculation device outputs the pseudo dutyvalue, which is prepared by decreasing the update duty value of eachphase so as to make the on-state time of the low voltage side switchingdevices of all three phases longer than the minimum detection time, whenthe on-state time of the low voltage side switching device of at leastone of phases, which corresponds to the update duty value, is smallerthan the minimum detection time.